1. Field of the Invention
The present invention relates to a tracking image pickup device and a tracking control method therefor, which is capable of tracking a tracking target while changing an image pickup direction, as well as a control program for implementing the tracking control method.
2. Description of the Related Art
Conventionally, there have been proposed various kinds of tracking image pickup devices that use an image pickup device and are capable of detecting a tracking object and performing tracking control of an image pickup direction such that the image of the object is brought e.g. to a central part of a screen.
In general, in a tracking image pickup device of the above-mentioned types a panning (horizontal) drive mechanism and a tilting (vertical) drive mechanism are controlled so as to reduce the amount of deviation between the position of an object as a tracking target and an image pickup direction. This control will be described with reference to FIG. 19.
FIG. 19 is a flowchart of a general panning and tilting control process executed by a conventional tracking image pickup device (which will be referred to as “the prior art 1”).
First, when the power of the system is turned on, or in response to a user's instruction or the like, the process is started (step S901). Then, initialization is performed e.g. by moving a panning mechanism and a tilting mechanism to a turning center (step S902). Thereafter, a tracking target is detected based on the characteristics of a tracking object (step S903), and the difference between the position of the detected tracking target and the image pickup direction, i.e. the difference between a panning direction and a tilting direction is calculated. Further, a control signal corresponding to the deviation is calculated (step S904), and the panning mechanism and the tilting mechanism are driven by the control signal (step S905). Then, the steps S903 to S905 are repeatedly carried out, whereby tracking image pickup of the object is enabled.
Further, a tracking device has been disclosed which is capable of changing a servo coefficient according to a zoom magnification (lens view angle range) of a photographic lens (see e.g. Japanese Patent No. 3610604, which will be referred to as “the prior art 2”). In the case where the relation between deviation of an object as a tracking target from the center of a screen and the amount of motor control is held constant without regard to a zoom magnification, when the zoom magnification is high, an apparatus or a device becomes excessively responsive to the movement of the object, which causes unstable control. On the other hand, when the zoom magnification is low, operation of the device becomes slow, making it difficult to move the image of the object to the screen center, so that the object can easily be missed. The tracking device according to the prior art 2 is capable of performing tracking control based on an appropriate parameter of a servo system corresponding to a zoom magnification.
Furthermore, a tracking image pickup device has been proposed which is capable of picking up the image of a moving object by tracking the object while changing its imaging magnification (see e.g. Japanese Laid-Open Patent Publication (Kokai) No. H11-122526, which will be referred to as “the prior art 3”). In this tracking image pickup device, each of a tilt rotation unit and a pan rotation unit is comprised of a rough rotation part and a fine rotation part. For wide-angle image pickup operation, the rough rotation part is operated, while for enlarged image pickup operation, the fine rotation part is operated. The fine rotation part which uses a laminated piezoelectric element is capable of performing fine adjustment in an image pickup direction without causing vibration due to motor rotation. Further, since the laminated piezoelectric element is directly driven, the fine rotation part can be driven at high speed.
However, during panning control, the prior arts 1 and 2 rotationally control a whole image pickup system including a lens, a lens barrel (a lens holding member, an autofocus driving part, a zoom driving part, etc.), an image pickup sensor, and a tilting mechanism (this image pickup system will be hereinafter referred to as “the panning image pickup system”). On the other hand, during tilting control, they rotationally control a whole image pickup system including the lens, the lens barrel, the image pickup sensor, and a panning mechanism (this image pickup system will be hereinafter referred to as “the tilting image pickup system”).
For this reason, the rotational speed of the panning image pickup system or the tilting image pickup system is influenced by the balance between the moment of inertia of the associated image pickup system and its drive mechanism, and a driving actuator. In other words, it is required to reduce the moment of inertia of the image pickup system and its drive mechanism to speed up panning drive or tilting drive. To reduce the moment of inertia, the thickness of each component part is reduced to reduce the weight of each part. However, the reduction of the thickness of each component part causes degradation of the rigidity of the device. When the rigidity of the device is degraded, the natural frequency of the device is lowered to a low frequency range, which results in degradation of responsivity of the control system of the device.
Thus, in the prior arts 1 and 2, so as to achieve high-speed tracking control by increasing the speed of panning drive or tilting drive, apparatus rigidity is often sacrificed, which makes it difficult to design the device.
In contrast, the prior art 3 can attain more stable and high-speed fine adjustment by fine movement and rough movement. However, since the laminated piezoelectric element is used, the fine adjustment is limited to a considerably small range.